The aging animal core (B) is a shared resource which supports animal model studies for all projects (1, 2, 3, 4, 5,) utilizing animals. One specific aim of this core is to provide specialized maintenance of barrier sustained transplant, conventional aged, caloric restricted and control aging rats. In addition, other specialized core services are provided to program investigators including gross and histopathological evaluations of experimental animals, serological surveillance to document a continuing virus (especially parvo virus) and mycoplasma disease free status and continuous consultation on laboratory animal genetics, modeling and spontaneous disease evaluations in aged rats. A third specific aim is to develop and provide for investigations in projects one and four, nutritionally (caloric) restricted aged (30 months) Sprague/Dawley and Fisher-344 rats.